1. Field of the Invention
The present invention relates to a so-called spin-valve type thin-film device, in which an electrical resistance thereof varies depending on the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic field, and, more particularly, to a magnetoresistive-effect device that allows a sense current to effectively flow through a multilayer film and a method for manufacturing the magnetoresistive-effect device.
2. Description of the Related Art
FIG. 33 is a cross-sectional view showing the construction of a conventional magnetoresistive-effect device, viewed from an ABS (air bearing surface) side thereof.
The magnetoresistive-effect device shown in FIG. 33 is the one called a spin-valve type thin-film device, one of the GMR (giant magnetoresistive) devices employing the giant magnetoresistive effect, and detects a magnetic field recorded on a recording medium, such as a hard disk.
This spin-valve type thin-film device includes a multilayer film 9 including a substrate 6, an antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic electrically conductive 3, a free magnetic layer 4, and a protective layer 7, a pair of hard bias layers 5, and a pair of electrode layers 8 and 8 respectively deposited on the hard bias layers 5 and 5, deposited on both sides of the multilayer film 9. The substrate 6 and the protective layer 7 are made of Ta (tantalum). A track width Tw is determined by the width dimension of the top surface of the multilayer film 9.
The antiferromagnetic layer 1 is typically an Fexe2x80x94Mn (iron-manganese) alloy film or an Nixe2x80x94Mn (nickel-manganese) alloy film, the pinned magnetic layer 2 and the free magnetic layer 4 are typically an Nixe2x80x94Fe (nickel-iron) alloy film, the nonmagnetic electrically conductive layer 3 is typically a Cu (copper) film, the hard bias layers 5 and 5 are typically Coxe2x80x94Pt (cobalt-platinum) alloy films, and the electrode layers 8 and 8 are typically Cr (chromium) films.
Referring to FIG. 33, the magnetization of the pinned magnetic layer 2 is placed into a single-domain state in the Y direction (i.e., the direction of a leakage magnetic field from a recording medium, namely, the direction of the height of the multilayer film from the recording medium), and the magnetization of the free magnetic layer 4 is oriented in the X direction under the influence of a bias magnetic field of the hard bias layers 5.
The magnetization of the pinned magnetic layer 2 is designed to be perpendicular to the magnetization of the free magnetic layer 4.
In this spin-valve type thin-film device, the electrode layers 8 and 8, deposited on the hard bias layers 5 and 5, feed sense currents to the pinned magnetic layer 2, the nonmagnetic electrically conductive layer 3 and the free magnetic layer 4. The direction of the advance of the recording medium, such as a hard disk, is aligned with the Z direction. When a leakage magnetic field is given by the recording medium in the Y direction, the magnetization of the free magnetic layer 4 varies from the X direction toward the Y direction. An electric resistance varies depending on the relationship between a variation in the magnetization direction within the free magnetic layer 4 and a pinned magnetization direction of the pinned magnetic layer 2 (this phenomenon is called the magnetoresistive effect), and the leakage magnetic field is sensed from the recording medium based on a variation in the voltage in response to the variation in the electrical resistance.
The magnetoresistive-effect device shown in FIG. 33 suffers from the following problems.
The magnetization of the pinned magnetic layer 2 is pinned in a single-domain state in the Y direction, and the hard bias layers 5 and 5, magnetized in the X direction, are arranged on both sides of the pinned magnetic layer 2. The magnetization of the pinned magnetic layer 2 on both ends is therefore affected by the bias magnetic field from the hard bias layers 5 and 5, and is thus not pinned in the Y direction.
Specifically, the magnetization of the free magnetic layer 4 in the X direction single-domain state and the magnetization of the pinned magnetic layer 2 are not in a perpendicular relationship, particularly on end portions of the multilayer film 9, under the influence of the X direction magnetization of the hard bias layers 5 and 5. The magnetization of the free magnetic layer 4 is set to be perpendicular to the magnetization of the pinned magnetic layer 2 because the magnetization of the free magnetic layer 4 is easily varied in response to a weak external magnetic field, causing the electric resistance to greatly vary, and thereby enhancing reproduction gain. Furthermore, the perpendicular relationship results in output waveforms having a good symmetry.
Since the magnetization of the free magnetic layer 4 on end portions thereof is likely to be pinned under the influence of a strong magnetization of the hard bias layers 5 and 5, the magnetization of the free magnetic layer 4 less varies in response to an external magnetic field. As shown in FIG. 33, insensitive regions having a poor reproduction gain is formed in the end regions of the multilayer film 9.
A central portion other than the insensitive regions, of the multilayer film 9, substantially contributes to the reproduction of the recorded magnetic field, and is thus a sensitive region exhibiting the magnetoresistive effect. The width of the sensitive region is narrower than a track width Tw defined in the formation of the multilayer film 9 by the width dimension of the insensitive regions.
The multilayer film 9 of the magnetoresistive-effect device on both end portions thereof is thus associated with the insensitive regions that contribute nothing to the reproduction output, and these insensitive regions merely increases a direct current resistance (DCR).
In the magnetoresistive-effect device having the construction in which the electrode layers 8 and 8 are deposited on only both sides of the multilayer film 9 as shown in FIG. 33, the sense current from the electrode layers 8 and 8 easily flows into the hard bias layers 5 and 5, reducing the percentage of the current flowing into the multilayer film 9. The presence of the insensitive regions further substantially reduces the quantity of the sense current flowing into the sensitive region. The conventional magnetoresistive-effect device cannot feed an effective sense current to the sensitive region, and suffers from a drop in the reproduction output as the direct current resistance increases.
Accordingly, it is an object of the present invention to provide a magnetoresistive-effect device which reduces a direct current resistance by overlapping an electrode layer over an insensitive region of a multilayer film to improve reproduction characteristics, and a method for manufacturing the magnetoresistive-effect device.
According to a first aspect of the present invention, a magnetoresistive-effect device includes a multilayer film including an antiferromagnetic layer, a pinned magnetic layer, which is deposited on and in contact with the antiferromagnetic layer, and the magnetization direction of which is pinned through an exchange anisotropic magnetic field with the antiferromagnetic layer, and a free magnetic layer, separated from the pinned magnetic layer by a nonmagnetic electrically conductive layer, a pair of hard bias layers, deposited on both sides of the multilayer film, for orienting the magnetization direction of the free magnetic layer perpendicular to the magnetization direction of the pinned magnetic layer, and a pair of electrode layers respectively deposited on the hard bias layers, wherein the electrode layers extend over the multilayer film.
Preferably, the first magnetoresistive-effect device includes the multilayer film including the antiferromagnetic layer, the pinned magnetic layer, which is deposited on and in contact with the antiferromagnetic layer, and the magnetization direction of which is pinned through an exchange anisotropic magnetic field with the antiferromagnetic layer, and the free magnetic layer, separated from the pinned magnetic layer by the nonmagnetic electrically conductive layer, the pair of hard bias layers, deposited on both sides of the multilayer film, for orienting the magnetization direction of the free magnetic layer perpendicular to the magnetization direction of the pinned magnetic layer, and the pair of electrode layers respectively deposited on the hard bias layers, for feeding a sense current to the pinned magnetic layer, the nonmagnetic electrically conductive layer, and the free magnetic layer, wherein the multilayer film includes a central sensitive region which provides an excellent reproduction gain, exhibiting a substantial magnetoresistive effect and insensitive regions which are formed on both sides of the sensitive region, and provide a poor reproduction gain, exhibiting no substantial magnetoresistive effect, and wherein the electrode layers deposited on both sides of the multilayer film extend over the insensitive regions of the multilayer film.
Preferably, the multilayer film is fabricated by successively laminating the antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic electrically conductive layer, and the free magnetic layer in that order from below, the antiferromagnetic layer laterally extends from the layers laminated thereon, and a pair of hard bias layer, a pair of intermediate layers, and a pair of electrode layers are respectively laminated on a pair of metallic layers respectively deposited on the antiferromagnetic layers in laterally extending regions thereof.
According to a second aspect of the present invention, a magnetoresistive-effect device includes a multilayer film including a free magnetic layer, nonmagnetic electrically conductive layer respectively lying over and under the free magnetic layer, pinned magnetic layers respectively lying over the one nonmagnetic electrically conductive layer and under the other nonmagnetic electrically conductive layer, each having a pinned magnetization direction, and antiferromagnetic layers respectively lying over the one pinned magnetic layer and under the other pinned magnetic layer, and a pair of hard bias layers, formed on both sides of the multilayer film, for orienting the magnetization direction of the free magnetic layer perpendicular to the magnetization direction of the pinned magnetic layer, and a pair of electrode layers respectively deposited on the hard bias layers, wherein the electrode layers extend over the multilayer film.
Preferably, the magnetoresistive-effect device includes the multilayer film including the free magnetic layer, nonmagnetic electrically conductive layers respectively lying over and under the free magnetic layer, pinned magnetic layers respectively lying over the one nonmagnetic electrically conductive layer and under the other nonmagnetic electrically conductive layer, each having a pinned magnetization direction, and antiferromagnetic layers respectively lying over the one pinned magnetic layer and under the other pinned magnetic layer, and the pair of hard bias layers, deposited on both sides of the multilayer film, for orienting the magnetization direction of the free magnetic layer perpendicular to the magnetization direction of the pinned magnetic layer, and the pair of electrode layers deposited on the hard bias layers, for feeding a sense current to the pinned magnetic layer, the nonmagnetic electrically conductive layer, and the free magnetic layer, wherein the multilayer film includes a central sensitive region which provides an excellent reproduction gain, exhibiting a substantial magnetoresistive effect and insensitive regions which are formed on both sides of the sensitive region, and provide a poor reproduction gain, exhibiting no substantial magnetoresistive effect, and wherein the electrode layers deposited on both sides of the multilayer film extend over the insensitive regions of the multilayer film.
Preferably, the free magnetic layer includes a plurality of soft magnetic thin films having different magnetic moments and nonmagnetic material layers, which are alternately laminated with one soft magnetic thin film separated from another by one nonmagnetic material layer, and the free magnetic layer is in a ferrimagnetic state in which the magnetization directions of two adjacent soft magnetic thin films, separated by the nonmagnetic material layer, are aligned antiparallel to each other. This arrangement offers the same result as the one obtained from the use of a thin free magnetic layer. The magnetization of the free magnetic layer is easily varied, improving the magnetic field detection sensitivity of the magnetoresistive-effect device.
The magnitude of the magnetic moment of the soft magnetic thin film is the product of the saturation magnetization (Ms) and the film thickness (t) of the soft magnetic thin film.
When the free magnetic layer is fabricated by alternately laminating a plurality of soft magnetic thin films having different magnetic moments and nonmagnetic material layers, the magnetization directions of two adjacent soft magnetic thin films, separated by the nonmagnetic material layer, are aligned antiparallel to each other in a ferrimagnetic state. With this arrangement, the plurality of the soft magnetic thin films alternate between the one having magnetization thereof aligned in the direction of a magnetic field generated from the bias layer and the one having magnetization thereof in 180 degrees opposite direction from the direction of the magnetic field of the bias layer.
The soft magnetic thin film having a magnetization direction thereof 180 degrees opposite from the direction of the magnetic field of the bias layer is subject to disturbance in magnetization direction on both end portions magnetically coupled with the bias layer. The soft magnetic thin film, separated from the above soft magnetic thin film by the nonmagnetic material layer, and having a magnetization direction thereof aligned with the direction of the magnetic field of the bias layer, is disturbed along therewith in magnetization direction on both end portions.
Both end portions where the soft magnetic thin films constituting the free magnetic field are disturbed in magnetization direction become insensitive regions which present a poor reproduction gain and exhibit no substantial magnetoresistive effect. In the present invention, the electrode layers are formed to extend over the insensitive regions.
When the free magnetic layer is fabricated by alternately laminating a plurality of soft magnetic thin films having different magnetic moments and nonmagnetic material layers with one nonmagnetic layer interposed between two adjacent soft magnetic thin films, the magnetic coupling junction between the multilayer film and the bias layer is preferably fabricated of an interface of the bias layer with the end face of only one of the plurality of the soft magnetic thin films forming the free magnetic layer.
It is sufficient if the bias layer aligns the magnetization direction of one of the plurality of the soft magnetic thin films constituting the free magnetic layer. When the magnetization direction of the one soft magnetic thin film is aligned in one direction, another soft magnetic thin film next to the first soft magnetic thin film is shifted to a ferrimagnetic state with a magnetization direction thereof aligned antiparallel. Consequently, all soft magnetic thin films are alternately aligned parallel to and antiparallel to one direction, and the magnetization direction of the entire free magnetic layer is aligned in one direction.
If the bias layer is magnetically coupled with the plurality of the soft magnetic thin films constituting the free magnetic layer, the magnetization direction of the soft magnetic thin films is undesirably disturbed on both end portions.
The pinned magnetic layer is fabricated by alternately laminating a plurality of soft magnetic thin films having different magnetic moments and nonmagnetic material layers with one nonmagnetic layer interposed between two adjacent soft magnetic thin films. When the magnetization direction of one soft magnetic thin film, separated from another soft magnetic thin film by the nonmagnetic material layer, is in a ferrimagnetic state with a magnetization direction thereof aligned antiparallel, the plurality of the soft magnetic thin films constituting the pinned magnetic layer mutually pin each other. As a result, the magnetization direction of the pinned magnetic layer is advantageously stabilized in one direction.
Here again, the magnitude of the magnetic moment of the soft magnetic thin film is the product of the saturation magnetization (Ms) and the film thickness (t) of the soft magnetic thin film.
The nonmagnetic material layer is preferably made of a material selected from the group consisting of Ru, Rh, Ir, Cr, Re, Cu, and alloys thereof.
The antiferromagnetic layer is preferably made of a PtMn alloy. Alternatively, the antiferromagnetic layer may be made of an Xxe2x80x94Mn alloy where X is a material selected from the group consisting of Pd, Ir, Rh, Ru, and alloys thereof, or may be made of a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy where Xxe2x80x2 is a material selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, and alloys thereof.
According to a third aspect of the present invention, a magnetoresistive-effect device includes a multilayer film including a magnetoresistive-effect layer, a soft magnetic layer, and a nonmagnetic layer with the magnetoresistive-effect layer and the soft magnetic layer laminated with the nonmagnetic layer interposed therebetween, a pair of hard bias layers deposited on both sides of the multilayer film, and a pair of electrode layers respectively deposited on the hard bias layers, wherein the electrode layers extend over the multilayer film.
Preferably, the magnetoresistive-effect device preferably includes the multilayer film including the magnetoresistive-effect layer, the soft magnetic layer, and the nonmagnetic layer with the magnetoresistive-effect layer and the soft magnetic layer laminated with the nonmagnetic layer interposed therebetween, the pair of hard bias layers deposited on both sides of the multilayer film, and the pair of electrode layers respectively deposited on the hard bias layers, wherein the multilayer film includes a central sensitive region which provides an excellent reproduction gain, exhibiting a substantial magnetoresistive effect and insensitive regions which are formed on both sides of the sensitive region, and provide a poor reproduction gain, exhibiting no substantial magnetoresistive effect, and wherein the electrode layers deposited on both sides of the multilayer film extend over the insensitive regions of the multilayer film.
Preferably, the position of at least one of the top edge and the bottom edge of the magnetic coupling junction between the multilayer film and the bias layer in the direction of the movement of a medium is at the same level as the position of at least one of the top surface and the bottom surface of the free magnetic layer or the magnetoresistive-effect layer in the direction of the movement of the medium.
Preferably, the bias layer is magnetically coupled, directly or via another intervening layer as an underlayer, with the multilayer film on the side face thereof transverse to the direction of a track width. The bias layer functions to align the magnetization direction of the free magnetic layer or the magnetoresistive-effect layer, out of the multilayer film, in one direction. It is therefore sufficient if the bias layer is magnetically coupled with the free magnetic layer only or the magnetoresistive-effect layer only. To prevent the magnetic field generated from the bias layer from affecting the magnetization direction of the pinned magnetic layer, the bias layer preferably remains magnetically uncoupled with the pinned magnetic layer.
A protective layer, constructed of Ta, etc., is preferably deposited, as a top layer, on top of the multilayer film to prevent oxidation.
An electrode layer, if laminated on the protective layer, adversely affects the characteristics of the magnetoresistive-effect device, for example, increases an electrical resistance. Therefore, the protective layer is preferably deposited where there is no junction between the multilayer film and the electrode layer.
The sensitive region of the multilayer film is defined as a region which results in an output equal to or greater than 50% of a maximum reproduction output while the insensitive regions of the multilayer film are defined as regions, formed on both sides of the sensitive region, which result in an output smaller than 50% of the maximum reproduction output, when the magnetoresistive-effect device having the electrode layers on both sides only of the multilayer film scans a micro track, having a signal recorded thereon, in the direction of a track width.
The width dimension of the sensitive region of the multilayer film is preferably equal to an optical track width O-Tw.
The width dimension of a portion of each electrode layer extending over the multilayer film is preferably within a range from 0 xcexcm to 0.08 xcexcm.
The width dimension of the portion of each electrode layer extending over the multilayer film is preferably equal to or larger than 0.05 xcexcm.
The angle made between the surface of the protective layer or the surface of the multilayer film with the protective layer removed therefrom and the end face of the electrode layer extending over the insensitive region of the multilayer film is preferably within a range of 20 degrees to 60 degrees, and more preferably within a range of 25 degrees to 45 degrees.
An insulator layer is preferably deposited between the electrode layers, which are deposited above and on both sides of the multilayer film, and the end face of the insulator layer is in direct contact with each of the electrode layers or is separated from each of the electrode layers by a layer.
The angle made between the surface of the protective layer or the surface of the multilayer film with the protective layer removed therefrom and the end face of the electrode layer extending over the insensitive region of the multilayer film is preferably 60 degrees or greater, and more preferably 90 degrees or greater.
The width dimension of a portion of each electrode layer extending over the multilayer film is preferably substantially equal to the width dimension of the insensitive region of the multilayer film.
According to a fourth aspect of the present invention, a method for manufacturing a magnetoresistive-effect device includes the steps of laminating, on a substrate, a multilayer film for exhibiting the magnetoresistive effect, depositing, on a sensitive region of the multilayer film, a lift-off resist layer having an undercut on the underside thereof facing insensitive regions of the multilayer film with the sensitive and insensitive regions beforehand measured through a micro track profile method, depositing bias layers on both sides of the multilayer film and magnetizing the bias layer in the direction of a track width, depositing an electrode layer on the bias layer at a slant angle with respect to the multilayer film, with the electrode layer formed into the undercut on the underside of the resist layer arranged on the multilayer film, and removing the resist layer from the multilayer film.
When a protective layer is deposited as a top layer on the multilayer film for oxidation prevention in the step of laminating, on the substrate, the multilayer film for exhibiting the magnetoresistive effect, the method preferably includes the steps of depositing the lift-off resist layer on top of the protective layer in the sensitive region of the multilayer film, in the step of depositing the lift-off resist layer on the sensitive region of the multilayer film, and exposing the underlayer beneath the protective layer by removing a portion of the protective layer which is not in direct contact with the lift-off resist layer. In this way, the electrode layer advantageously joins the multilayer film where the protective layer having a high electrical resistance is removed, when the electrode layer is deposited to extend over the multilayer film.
In the step of depositing the electrode layer, the angle made between the surface of the protective layer or the surface of the multilayer film with the protective layer removed therefrom and the end face of the electrode layer extending over the insensitive region of the multilayer film is preferably within a range of 20 degrees to 60 degrees, and more preferably within a range of 25 degrees to 45 degrees.
According to a fifth aspect of the present invention, a method for manufacturing a magnetoresistive-effect device includes the steps of laminating, on a substrate, a multilayer film for exhibiting the magnetoresistive effect, depositing an insulator layer on the multilayer film, depositing, on the insulator layer in a sensitive region of the multilayer film, a lift-off resist layer having an undercut on the underside thereof facing insensitive regions of the multilayer film with the insensitive regions beforehand measured through a micro track profile method, removing the insulator layer deep to the undercut formed on the underside of the resist layer, through etching, depositing bias layers on both sides of the multilayer film and magnetizing the bias layers in the direction of a track width, depositing an electrode layer on the bias layer at a slant angle with respect to the multilayer film, with the electrode layer formed to be in direct contact with an end face of the insulator layer, i.e., the underlayer beneath the resist layer, or with the electrode layer formed to be separated from the end face of the insulator layer by a layer, and removing the resist layer from the insulator layer.
When a protective layer is deposited as a top layer on the multilayer film for oxidation prevention in the step of depositing, on the substrate, the multilayer film for exhibiting the magnetoresistive effect, the method preferably includes the step of removing the area of the protective layer not covered with the insulator layer to expose the underlayer beneath the protective layer, subsequent to the step of removing the insulator layer deep to the undercut formed on the underside of the resist layer through etching. In this way, the electrode layer advantageously joins the multilayer film where the protective layer having a high electrical resistance is removed, when the electrode layer is formed to extend over the multilayer film.
In the method for manufacturing the magnetoresistive-effect device including the step of laminating the insulator layer on the multilayer film, in the step of forming the electrode layer, the angle made between the surface of the protective layer or the surface of the multilayer film with the protective layer removed therefrom and the end face of the electrode layer extending over the insensitive region of the multilayer film is preferably 60 degrees or greater, and more preferably 90 degrees or greater.
The sensitive region of the multilayer film, measured through a micro track profile method, is defined as a region which results in an output equal to or greater than 50% of a maximum reproduction output while the insensitive regions of the multilayer film are defined as regions, formed on both sides of the sensitive region, which result in an output smaller than 50% of the maximum reproduction output, when a magnetoresistive-effect device having the electrode layers formed on hard bias layers only and not extending over the multilayer film scans a micro track, having a signal recorded thereon, in the direction of the track width.
In the method for manufacturing a magnetoresistive-effect device, the bias layers are preferably deposited on both sides of the multilayer film through at least one sputtering technique selected from an ion-beam sputtering method, a long-throw sputtering method, and a collimation sputtering method, with the substrate, having the multilayer film thereon, placed perpendicular to a target made of a composition of the bias layer, and the electrode layer is preferably deposited on the bias layer into an undercut formed in the underside of the resist layer arranged on the multilayer film through at least one sputtering technique selected from an ion beam sputtering method, a long-throw sputtering method, and a collimation sputtering method, with the substrate, having the multilayer film thereon, placed slightly oblique to a target made of a composition of the electrode layer, or with the target placed slightly oblique to the substrate.
Preferably, the multilayer film includes an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically conductive layer, and a free magnetic layer, or the multilayer film includes a free magnetic layer, nonmagnetic electrically conductive layers respectively lying over and under the free magnetic layer, pinned magnetic layers respectively lying over the one nonmagnetic electrically conductive layer and under the other nonmagnetic electrically conductive layer, and antiferromagnetic layers respectively lying over the one pinned magnetic layer and under the other pinned magnetic layer, or the multilayer film includes a magnetoresistive-effect layer, a soft magnetic layer, and a nonmagnetic layer wherein the magnetoresistive-effect layer and the soft magnetic layer are laminated with the nonmagnetic layer interposed therebetween.
Preferably, the multilayer film includes at least one of each of an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically conductive layer, and a free magnetic layer, or the multilayer film includes a free magnetic layer, nonmagnetic electrically conductive layers respectively lying over and under the free magnetic layer, pinned magnetic layers respectively lying over the one nonmagnetic electrically conductive layer and under the other nonmagnetic electrically conductive layer, and antiferromagnetic layers respectively lying over the one pinned magnetic layer and under the other pinned magnetic layer, or the multilayer film includes a magnetoresistive-effect layer, a soft magnetic layer, and a nonmagnetic layer wherein the magnetoresistive-effect layer and the soft magnetic layer are laminated with the nonmagnetic layer interposed therebetween.
The free magnetic layer preferably includes a plurality of soft magnetic thin films having different magnetic moments and nonmagnetic material layers, which are alternatively laminated with one soft magnetic thin film separated from another by one nonmagnetic material layer, and the free magnetic layer is in a ferrimagnetic state in which the magnetization directions of adjacent soft magnetic thin films, separated by the nonmagnetic material layer, are aligned antiparallel to each other.
When the free magnetic layer is fabricated by laminating the plurality of soft magnetic thin films having different magnetic moments and the nonmagnetic material layers with one nonmagnetic material layer interposed between adjacent soft magnetic thin films, the magnetic coupling junction between the multilayer film and the bias layer is preferably fabricated of an interface with the end face of only one of the plurality of the soft magnetic thin films forming the free magnetic layer, in the step of depositing the bias layer.
The pinned magnetic layer preferably includes a plurality of soft magnetic thin films having different magnetic moments and nonmagnetic material layers, which are alternately laminated with one soft magnetic thin film separated from another by one nonmagnetic material layer, and the pinned magnetic layer is in a ferrimagnetic state in which the magnetization directions of adjacent soft magnetic thin films, separated by the nonmagnetic material layer, are aligned antiparallel to each other.
The nonmagnetic material layer is preferably made of a material selected from the group consisting of Ru, Rh, Ir, Cr, Re, Cu, and alloys thereof.
In the step of depositing the bias layers, the position of at least one of the top edge and the bottom edge of the magnetic coupling junction between the multilayer film and the bias layer in the direction of the movement of a medium is preferably set to be at the same level as the position of at least one of the top surface and the bottom surface of the free magnetic layer or the magnetoresistive-effect layer in the direction of the movement of the medium.
The antiferromagnetic layer is preferably made of a PtMn alloy. Alternatively, the antiferromagnetic layer may be made of an Xxe2x80x94Mn alloy where X is a material selected from the group consisting of Pd, Ir, Rh, Ru, and alloys thereof, or may be made of a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy where Xxe2x80x2 is a material selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, and alloys thereof.
Even if the width dimension of the top surface of the multilayer film, composed of the antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic electrically conductive layer, and the free magnetic layer, is defined as a track width Tw, the full width of the multilayer film does not necessarily exhibit the magnetoresistive effect. only the central portion of the width of the multilayer film offers an excellent reproduction gain, exhibiting the magnetoresistive effect in practice. The central portion of the multilayer film having an excellent reproduction gain is called a sensitive region, and the remaining portions, formed on both sides of the sensitive region, and having a poor reproduction gain, are called insensitive regions. The sensitive region and the insensitive regions are measured using a micro track profile method. Referring to FIG. 31, the micro track profile method is discussed.
As shown in FIG. 31, the conventional magnetoresistive-effect device (see FIG. 33), including the multilayer film exhibiting the magnetoresistive effect, the hard bias layers on both sides of the multilayer film, and the electrode layers formed on the hard bias layers, is formed on the substrate. The electrode layers are formed on only both sides of the multilayer film.
The width dimension A of the top surface of the multilayer film not covered with the electrode layers is measured through an optical microscope. The width dimension A is defined as a track width Tw measured through an optical method (hereinafter referred to as an optical track width dimension O-Tw).
A signal is recorded onto a micro track on the recording medium. A magnetoresistive-effect device is set to scan the micro track in the direction of a track width, and the relationship between the width dimension A and the reproduction output is measured. Alternatively, the recording medium having the micro track may be set to scan the magnetoresistive-effect device in the direction of the track width to measure the relationship between the width dimension A of the multilayer film and the reproduction output. The measurement results are shown in the lower portion of FIG. 31.
From the measurement results, the reproduction output rises high at the center of the multilayer film, and gets lower toward edges thereof. The central portion of the multilayer film exhibits an excellent magnetoresistive effect, and contributes to the reproduction capability, while edge portions of the multilayer film suffers from a poor magnetoresistive effect, resulting a low reproduction output with an insufficient reproduction capability.
The portion, having a width dimension B on the multilayer film and generating an output equal to or greater than 50% of a maximum reproduction output, is defined as the sensitive region, and the portion, having a width dimension C on the multilayer film and generating an output smaller than 50% of the maximum reproduction output, is defined as the insensitive region.
Since the insensitive region offers no effective reproduction capability, and merely raises a direct current resistance (DCR), the electrode layer is set to extend over the insensitive region in the present invention. In this arrangement, the junction areas of the multilayer film with the hard bias layers and the electrode layers, formed on both sides of the multilayer film, are increased. A sense current from the electrode easily flows into the multilayer film without passing through the hard bias layer, the direct current resistance is reduced, and the reproduction characteristics are thus improved.
As described above, when electrode layers 210 and 210 are overlapped onto a multilayer film 209 as shown in FIG. 34, the electrode layers 210 and 210 are connected to the multilayer film 209, permitting a sense current to effectively flow into the multilayer 209 from the electrode layer 210.
In order to cause a sense current to effectively flow into the multilayer film 209 from the electrode layer 210, the thickness of the electrode layer 210 must be larger than before, the thickness h1 of the electrode 210 on and in direct contact with the multilayer film 209 must be larger, and the direct current resistance of the electrode layer 210 must be reduced.
If the thickness h1 of the electrode layer 210 is small relative to that of the multilayer film 209, the direct current resistance of the electrode layer 210 rises, more likely causing the sense current from the electrode layer 210 to shunt to a hard bias layer 205. As a result, the reproduction output can drop.
With the electrode layer 210 overlapped onto the multilayer film 209 and the thickness h1 of the electrode layer 210 increased relative to the thickness of the multilayer film 209, the shunt of the sense current to the hard bias layer 205 is controlled, and the sense current effectively flows from the electrode layer 210 to the multilayer film 209.
If the electrode layer 210 having a thickness h1 is deposited on the top surface of the multilayer film 209, a large step develops between the top surface of the electrode layer 210 and the top surface of the multilayer film 209. When an upper gap layer 211, made of an insulator material, covers throughout the electrode layer 210 and the multilayer film 209, the upper gap layer 211 suffers a poor step coverage, and a film discontinuity occurs at the step. As a result, the upper gap layer 211 fails to provide sufficient insulation.
It is yet another object of the present invention to provide a magnetoresistive-effect device which increases reproduction output by reducing a current loss caused by a sense current flowing into a hard bias layer, while making dominant a sense current flowing into a sensitive region occupying the central portion of a multilayer film, and which permits an upper gap layer to be deposited with proper insulation assured.
According to a sixth aspect of the present invention, a magnetoresistive-effect device includes a multilayer film including an antiferromagnetic layer, a pinned magnetic layer, which is deposited on and in contact with the antiferromagnetic layer, and the magnetization direction of which is pinned through an exchange anisotropic magnetic field with the antiferromagnetic layer, and a free magnetic layer, separated from the pinned magnetic layer by a nonmagnetic electrically conductive layer, a pair of hard bias layers, deposited on both sides of the multilayer film, for orienting the magnetization direction of the free magnetic layer perpendicular to the magnetization direction of the pinned magnetic layer, and a pair of electrode layers respectively deposited on the hard bias layers, wherein an intermediate layer, made of at least one of a high-resistivity material having a resistance higher than that of the electrode layer and an insulating material, is interposed between each of the hard bias layers and each of the electrode layers, and the electrode layers extend over the multilayer film.
The multilayer film is preferably fabricated by successively laminating the antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic electrically conductive layer, and the free magnetic layer in that order from below, the antiferromagnetic layer laterally extends from the layers laminated thereon, and a pair of hard bias layer, a pair of intermediate layers, and a pair of electrode layers are respectively laminated on a pair of metallic layers respectively deposited on the antiferromagnetic layers in the laterally extending regions thereof.
According to a seventh aspect of the present invention, a magnetoresistive-effect device includes a multilayer film including a free magnetic layer, nonmagnetic electrically conductive layers respectively lying over and under the free magnetic layer, pinned magnetic layers respectively lying over the one nonmagnetic electrically conductive layer and under the other nonmagnetic electrically conductive layer, each having a pinned magnetization direction, and antiferromagnetic layers respectively lying over the one pinned magnetic layer and under the other pinned magnetic layer, and a pair of hard bias layers, deposited on both sides of the multilayer film, for orienting the magnetization direction of the free magnetic layer perpendicular to the magnetization direction of the pinned magnetic layer, and a pair of electrode layers respectively deposited on the hard bias layers, wherein an intermediate layer, made of at least one of a high-resistivity material having a resistance higher than that of the electrode layer and an insulating material, is interposed between each of the hard bias layers and each of the electrode layers and the electrode layers extend over the multilayer film.
The antiferromagnetic layer is preferably made of a PtMn alloy. Alternatively the antiferromagnetic layer may be made of an Xxe2x80x94Mn alloy where X is a material selected from the group consisting of Pd, Ir, Rh, Ru, and alloys thereof, or may be made of a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy where Xxe2x80x2 is a material selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, and alloys thereof.
According to an eighth aspect of the present invention, a magnetoresistive-effect device includes a multilayer film including a magnetoresistive-effect layer, a soft magnetic layer, and a nonmagnetic layer with the magnetoresistive-effect layer and the soft magnetic layer laminated with the nonmagnetic layer interposed therebetween, a pair of hard bias layers deposited on both sides of the multilayer film, and a pair of electrode layers respectively deposited on the hard bias layers, wherein an intermediate layer, made of at least one of a high-resistivity material having a resistance higher than that of the electrode layer and an insulating material, is interposed between each of the hard bias layers and each of the electrode layers and the electrode layers extend over the multilayer film.
The high-resistivity material, which fabricates the intermediate layer interposed between the hard bias layer and the electrode layer, is preferably at least one material selected from the group consisting of TaSiO2, TaSi, CrSiO2, CrSi, WSi, WSiO2, TiN, and TaN.
Alternatively, the high-resistivity material, which fabricates the intermediate layer interposed between the hard bias layer and the electrode layer, is preferably at least one material selected from the group consisting of Al2O3, SiO2, Ti2O3, TiO, WO, AlN, Si3N4, B4C, SiC, and SiAlON.
The multilayer film preferably includes a central sensitive region which provides an excellent reproduction gain, exhibiting a substantial magnetoresistive effect and insensitive regions which are formed on both sides of the sensitive region, and provide a poor reproduction gain, exhibiting no substantial magnetoresistive effect, wherein the electrode layers deposited on both sides of the multilayer film extend over the insensitive regions of the multilayer film.
The sensitive region of the multilayer film is defined as a region which results in an output equal to or greater than 50% of a maximum reproduction output while the insensitive regions of the multilayer film are defined as regions, formed on both sides of the sensitive region, which result in an output smaller than 50% of the maximum reproduction output, when the magnetoresistive-effect device having the electrode layers on both sides only of the multilayer film scans a micro track, having a signal recorded thereon, in the direction of a track width.
The width dimension of the sensitive region of the multilayer film is preferably equal to an optical track width O-Tw.
It is another object of the present invention to provide a magnetoresistive-effect device which restricts a sense current from shunting to a hard bias layer while assuring sufficient insulation in an upper gap layer. To achieve this object, the present invention employs an intermediate layer, made of a high-resistivity material having a resistance higher than that of the electrode layer or an insulating material, interposed between each of the hard bias layers and each of the electrode layers, and the electrode layers extend over the multilayer film.
The intermediate layer of an insulator material interposed between the hard bias layer and the electrode layer reduces a sense current shunting into the hard bias layer (i.e., a current loss). With the electrode layer extending over the multilayer film, the electrode layer is connected to the multilayer film on the top surface thereof, thereby permitting the sense current to directly flow from the electrode layer to the multilayer film.
In accordance with the first through third aspects of the present invention, the electrode layer 210 overlaps the multilayer film 209, but no intermediate layer is interposed between the electrode layer 210 and the hard bias layer 205. To allow the sense current to effectively flow from the electrode layer 210 to the multilayer film 209, the thickness h1 of the electrode layer 210 relative to the multilayer film 209 must be increased to reduce the direct current resistance of the electrode layer 210 and to restrict the sense current from shunting to the hard bias layer 205. In this case, a sharp step develops between the top surface of the electrode layer 210 and the top surface of the multilayer film 209. When an upper gap layer 211 of an insulator material covers the electrode layer 210 and the multilayer film 209, the upper gap layer 211 suffers a poor step coverage, and a film discontinuity occurs at the step. As a result, the upper gap layer 211 fails to provide sufficient insulation.
In accordance with the sixth through eighth aspects of the present invention, the intermediate layer of an insulator material is interposed between the hard bias layer and the electrode layer. The sense current is less likely to shunt from the electrode layer to the hard bias layer regardless of the thickness of the electrode layer. In contrast to the magnetoresistive-effect layer in accordance with the first through third aspects, the sense current effectively flows from the electrode layer to the multilayer film even if the thickness of the electrode layer is decreased relative to the thickness of the multilayer film. The magnetoresistive-effect device of the sixth through eighth aspects works with a thin electrode layer, thereby reducing a step height formed between the top surface of the electrode layer and the top surface of the multilayer film, improving a step coverage of the upper gap layer formed over the border area between the electrode layer and the multilayer film, and thereby providing sufficient insulation.
The multilayer films in a GMR (Giant Magnetoresistance) device and an AMR (Anisotropic Magnetoresistance) device offer a good gain in only a central portion thereof, rather than providing the magnetoresistive effect in the entire area thereof. Only the central portion is a substantially working area for exhibiting the magnetoresistive effect. The portion of the multilayer film having the excellent reproduction gain is called a sensitive region, and portions on both sides of the sensitive region are called insensitive regions. The ratios of the sensitive region and the insensitive regions respectively to the entire multilayer film is measured through the micro track profile method. The micro trap profile method has already been discussed.
Considering that the multilayer film is formed of the sensitive region and the insensitive regions, it is yet another object of the present invention to provide a magnetoresistive-effect device which allows the sense current to predominantly flow into the sensitive region having the substantial magnetoresistive effect. To achieve this object, the electrode layer overlapping the multilayer is set to extend over the insensitive region.
With the electrode layer extending over the insensitive region, the sense current is allowed to predominantly flow into the sensitive region rather than the insensitive regions. The reproduction output is thus increased.
However, the electrode layer extends over but must not reach the sensitive region. As will be discussed later, the electrode layer reaching the sensitive region leads to noise generation and reduction in the reproduction output.